U.S. patent number 4,598,106 [Application Number 06/714,391] was granted by the patent office on 1986-07-01 for pressure-resistant buoyancy material.
This patent grant is currently assigned to Nichiyu Giken Kogyo Co., Ltd., Nippon Oils & Fats Co., Ltd.. Invention is credited to Katsumi Utsugi.
United States Patent |
4,598,106 |
Utsugi |
July 1, 1986 |
Pressure-resistant buoyancy material
Abstract
A pressure-resistant buoyancy material, comprising
pressure-resistant hollow elements, a syntactic foam, and an empty
space intervening between the pressure-resistant hollow elements
and the syntactic foam, communicating with the outside of the
buoyancy material. The pressure-resistant hollow elements are
retained in a freely movable state in the empty space.
Inventors: |
Utsugi; Katsumi (Hidakamachi,
JP) |
Assignee: |
Nippon Oils & Fats Co.,
Ltd. (Tokyo, JP)
Nichiyu Giken Kogyo Co., Ltd. (Kawagoe, JP)
|
Family
ID: |
16980071 |
Appl.
No.: |
06/714,391 |
Filed: |
March 21, 1985 |
Foreign Application Priority Data
|
|
|
|
|
Nov 9, 1984 [JP] |
|
|
59-235032 |
|
Current U.S.
Class: |
523/218; 521/54;
523/219; 521/138; 521/182; 521/178 |
Current CPC
Class: |
B63B
3/13 (20130101); B63G 8/24 (20130101); F16L
23/02 (20130101) |
Current International
Class: |
B63B
3/13 (20060101); B63B 3/00 (20060101); F16L
23/02 (20060101); F16L 23/00 (20060101); C08J
009/32 () |
Field of
Search: |
;523/219,218
;521/54,138,178,182 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Foelak; Morton
Attorney, Agent or Firm: Oblon, Fisher, Spivak, McClelland
& Maier
Claims
What is claim is:
1. A pressure-resistant buoyancy material, which comprises two
identical molded pieces of unsaturated polyester resin or epoxy
resin syntactic foam containing uniform hemispheric depressions,
said pieces having been joined to each other so that each
hemisphere forms a spherically shaped cavity therein, where each
cavity contains therein a hollow pressure-resistant sphere which is
smaller in diameter than said cavity so that said sphere is freely
movable in said cavity, and further wherein each cavity
communicates with the outside of said molded pieces by way of an
empty path through said syntactic foam.
2. A buoyancy material according to claim 1, wherein each of said
hollow pressure-resistance spheres is made of ceramic material and
possesses a bulk modulus of at least 9.times.10.sup.3 kgf/mm.
3. A buoyancy material according to claim 1, wherein each of said
hollow pressure-resistance spheres has a volume which is 95% to
99.7% of the volume of each of said cavities.
4. A buoyancy material according to claim 1, wherein each of said
hollow pressure-resistant spheres has a diameter of at least 20 mm
and a specific gravity in the range of 0.2 to 0.5.
5. A buoyancy material according to claim 2, wherein said ceramic
material is selected from the group consisting of alumina ceramic
and zirconia ceramic.
Description
BACKGROUND OF THE INVENTION
This invention relates to a pressure-resistant buoyancy material to
be used mainly under water of great depth (hereinafter referred to
as "deep water").
In recent years, efforts are being continued for the development of
techniques for lowering various observation instruments to great
depths in the sea, operating them under water, and later raising
them to the surface. Such techniques are required for deep water
surveys conducted by submarines for economic and academic purposes.
The use of such instruments in the manner described above
necessitates a pressure-resistant buoyancy material of low specific
gravity and high enough strength to withstand severe working
conditions under deep water.
As pressure-resistant buoyancy materials capable of producing ample
buoyancy under deep water, hollow plastic spheres, hollow glass
spheres, syntactic foam compositions, etc. have been in use.
Use of hollow spheres made of metallic material is conceivable.
These hollow spheres, however, are not suitable as a buoyancy
material because they have a large specific gravity and low
buoyancy.
Among commercially available hollow plastic sphere buoyancy
materials is a product which is effectively usable under water at
depths up to 1500 meters (manufactured by Ube Resin Processing Co.,
Ltd. and marketed under trademark designation of "Cycolac Flote").
This hollow plastic sphere is made of ABS resin (compression
strength 480 kg/cm.sup.2) which measures 360 mm in diameter, weighs
10 kg, and has a specific gravity of 0.41.
Among commercially available hollow glass sphere buoyancy materials
is a product of Benthos Inc. in the United States, which measures
432 mm in diameter, weighs 17.7 kg, and has a specific gravity of
0.42 and a working water depth of 6000 m. The most serious drawback
suffered by any hollow glass sphere resides in the fact that it is
vulnerable to shocks.
As means of improving hollow glass spheres by eliminating this
serious drawback, the inventor has so far developed a
pressure-resistant buoyancy material formed of hollow ceramic
spheres and a pressure-resistant buoyancy material formed of hollow
ceramic spheres and syntactic foam composition (Japanese Patent
Application SHO No. 58(1983)-204729).
The hollow ceramic sphere involved in the invention just mentioned
is usable effectively as a buoyancy material under water of a
greater depth than the conventional hollow plastic sphere and
hollow glass sphere.
These hollow spheres, because of their peculiar shape, invariably
necessitate special devices for effective attachment to submarines,
which have only complicated contours available for contact with the
spheres.
As a convenient buoyancy material for a submarine, therefore, a
syntactic foam which is formed of hollow glass microspheres and
polyester resin or epoxy resin has found acceptance. Methods for
the production of such syntactic foam are disclosed in Japanese
Patent Disclosure SHO No. 49(1974)-58162, U.S. Pat. No. 3,477,967,
and Japanese Patent Disclosure SHO No. 57(1982)-28142, for
example.
The syntactic foam is obtained by pouring a raw material, which is
a mixture of hollow glass microspheres and thermosetting resin, in
a mold and allowing it to set. Thus, the syntactic foam can be
obtained in various shapes conforming exactly to the cavity of a
given mold. It therefore proves advantageous for use with a
submarine which necessitates a buoyancy material of complicated
shape as mentioned above.
The properties of the latest syntactic foam published in the
research report, JAMSTECTR 12 (1984), of the Ocean Science
Technology Center are shown in the following table.
______________________________________ High-strength Low-specific
type gravity type ______________________________________ Specific
gravity 0.561 0.545 Compression strength (kgf/cm.sup.2) 920 867
Crushing strength (kgf/cm.sup.2) 1276 1238
______________________________________
For any syntactic foam to withstand use under deep water of 6000 m,
the compressive strength and the crushing strength are required to
be about 900 kgf/cm.sup.2 and 1240 kgf/cm.sup.2 respectively, with
the safety factor calculated as 2. The high-strength type shown in
the table meets this requirement. The highest specific gravity
obtained by the technique of the existing standard is approximately
0.56.
Today ocean surveys are required to be conducted at still greater
depths. To meet the requirements, a need is felt for the
development of a buoyancy material, specifically a syntactic foam,
possessing lower specific gravity and higher strength.
For the purpose, it is considered to be necessary:
(1) to use hollow glass microspheres having lower specific gravity
and higher strength,
(2) to improve the packing factor (ratio of bulk to true particle
density) of the hollow glass microspheres, and
(3) to use resin of high strength.
In order to increase the strength of the hollow glass spheres it is
necessary to use glass of high rigidity, which is incompatible with
the aim of reducing specific gravity. The packing factor of the
hollow glass microspheres can be increased by combining spheres of
different diameters, but there is a limit to the degree of
compactness that can be obtained. When the product of 3M Corp.
marketed under the trademark "Glass Bubble F29x" is adopted and
100-micron and 30-micron grades of the product are mixed in a ratio
of 60:40 (so that the average specific gravity of the hollow glass
microspheres is about 0.28), for example, the packing factor is
73%. When the gaps separating the adjacent hollow microspheres are
filled up with resin of a specific gravity of 1.2, then the
produced syntactic foam has an overall specific gravity of 0.528.
If the specific gravity of this resin is lowered to decrease the
overall specific gravity of the syntactic foam, the syntactic foam
itself has the strength thereof proportionally lowered. Where the
specific gravity of the hollow microspheres and that of the resin
used in the syntactic foam are lowered, then the produced syntactic
foam has the strength thereof lowered consequently. It is not
possible to effect the desired decrease of specific gravity without
a sacrifice of the strength of the syntactic foam.
The inventor continued a study with a view to developing a buoyancy
material of improved performance and consequently developed the
aforementioned novel pressure-resistant buoyancy material formed of
hollow ceramic microspheres and a syntactic foam. This buoyancy
material has been filed for patent under Japanese Patent
Application SHO No. 58(1983)-204729. As compared with the
conventional syntactic foam, this buoyancy material permits further
reduction of specific gravity and further increase of strength and
is suitable for use under deep water. When the hollow ceramic
spheres and the syntactic foam are combined in intimate mutual
contact, the ratio of volume reduction under application of
pressure differs between the two components of the buoyancy
material because the ratio of voluminal elasticity is not equal
between them. The pressure so applied, therefore, is liable to
impair uniform distribution if stress and lower the overall
strength of the buoyancy material.
The present invention is characterized by disposing an empty space
in the boundary between the syntactic foam and the hollow ceramic
spheres thereby eliminating the disadvantage suffered by the
conventional buoyancy material formed of such two components.
SUMMARY OF THE INVENTION
The pressure-resistant buoyancy material of the present invention
comprises pressure-resistant hollow spheres and syntactic foam,
with an externally communicating empty space interposed between the
pressure-resistant hollow spheres and the syntactic foam.
In a typical embodiment of the present invention, the syntactic
foam contains an empty space communicating with the outside of the
foam and serving to hold the pressure-resistant hollow spheres in a
freely movable state. Thus, the pressure-resistant hollow spheres
enjoy freedom of motion within the empty space.
An object of this invention is to provide a buoyancy material which
consists of syntactic foam and pressure-resistant hollow spheres
and which exhibits outstanding resistance to pressure while
suffering no loss of strength even under deep water.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and features of this invention will become apparent
to those skilled in the art as the disclosure is made in the
following description of a preferred embodiment of the invention,
as illustrated in the accompanying drawings, in which:
FIG. 1 is a cross-sectional diagram illustrating a buoyancy
material of this invention; and
FIG. 2 is a cross-sectional diagram illustrating a buoyancy
material described in a Comparative Experiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the buoyancy material of the present invention will be
described below with reference to the accompanying drawings. FIG. 1
represents a typical pressure-resistant buoyancy material of this
invention and FIG. 2 a pressure-resistant buoyancy material
produced for the purpose of comparison by omitting the provision of
an empty space between the syntactic foam and the
pressure-resistant hollow spheres. In the drawings, 1 denotes a
pressure-resistant hollow sphere, 2 a syntactic foam, 3 an empty
space interposed between the syntactic foam 2 and the
pressure-resistant hollow sphere 1, 4 a path for communication of
the empty space with the outside of the pressure-resistant buoyancy
material, 5 a joint between the adjacent syntactic foam pieces, and
6 adhesive agent applied between the pressure-resistant hollow
sphere and the syntactic foam.
The difference between the buoyancy material of the present
invention illustrated in FIG. 1 and the buoyancy material for
comparison illustrated in FIG. 2 resides in the fact that the empty
space appearing in FIG. 1 is absent in FIG. 2 and the
pressure-resistant hollow sphere in FIG. 2 is fastened to the
syntactic foam through the medium of the adhesive agent.
Now, a typical method for manufacture of the buoyancy material of
the present invention is described below. First, the
pressure-resistant hollow spheres are produced. Then, the raw
material for the syntactic foam is cast in a molding die having
disposed therein a required number of hemispheres of a diameter
slightly larger than the outside of the pressure-resistant spheres.
Then, the raw material in the molding die is cured by application
of heat. After the curing by heating, the molding die is removed to
obtain a syntactic foam piece containing hemispherical cavities
therein. One more syntactic foam piece of entirely the same shape
is produced by repeating the procedure. The two syntactic foam
pieces so obtained are joined to each other as illustrated in FIG.
1, with the pressure-resistant hollow spheres placed one each in
the cavities. Finally, paths for communication between the empty
space and the outside are formed by mechanical working.
In the buoyancy material of the present invention, the syntactic
foam and the hollow spheres are not joined to each other but are
separated from each other by an intervening empty space and the
hollow spheres are retained in a freely movable state and the empty
space is allowed to communicate with the outside. When the buoyancy
material is placed under water, therefore, the pressure of the
surrounding medium, such as sea water, is free to enter the empty
space. Thus, the buoyancy material does not suffer any loss of
strength even when it is exposed to repeated application of
external pressure. The pressure-resistant hollow spheres are
desired to be made of ceramic material having a bulk modulus of at
least 9.times.10.sup.3 kgf/mm. The hollow spheres are desired to
have a diameter of not less than 20 mm and specific gravity of 0.2
to 0.5. Optionally, hollow cylinders of substantially the same
description can be used instead. The reason for the choice of the
specific magnitude of bulk modulus mentioned above is that the
decrease of buoyance under pressure is mitigated by lowering the
voluminal shrinkage. For the convenience of manufacture, the
diameter is desired to be not less than 20 mm and the specific
gravity to be not less than 0.2. If the specific gravity is greater
than 0.5, the buoyancy is lowered and the object of lowering
specific gravity is not fulfilled. As concerns the kind of ceramic
material, the ceramic material of alumina type or zirconia type
proves advantageous for use in the present invention. The syntactic
foam in the buoyancy material of this invention can be obtained by
any of the methods known to the art such as, for example, the
vacuum mixing method or the vacuum impregnation method which
effects combination of hollow glass microspheres and unsaturated
polyester resin or epoxy resin.
In the cavity of the syntactic foam, the pressure-resistant hollow
sphere is required to occupy 99.7% to 95% of the volume of the
cavity.
In other words, the difference between the volume of the cavity in
the syntactic foam and that of the pressure-resistant hollow
sphere, i.e. 0.3% to 5% of the volume of the cavity, represents the
empty space for admitting the external pressure medium. If this
empty space is smaller than 0.3%, the pressure applied to the
buoyancy material causes the syntactic foam to adhere tightly to
the pressure-resistant hollow sphere because the amount of
shrinkage of the syntactic foam is greater than that of the
pressure-resistant hollow sphere. Moreover, the syntactic foam
sustains cracks under increased pressure. If this empty space is
larger than 5%, however, there ensues the disadvantage that the
buoyancy is not sufficient.
Typical compositions of the syntactic foam usable advantageously
for this invention are shown below.
______________________________________ (1) (1) Hollow glass
microspheres (specific gravity 32 wt % of 0.32) (product of 3M
Corp., "Glass Bubbles, D 32/4500" in commercial designation) (2)
Unsaturated polyester resin (product of 67 wt % Nippon Shokubai
Kagaku Kogyo Co., Ltd., "Epolac G82" in commercial designation)
which comprises styrene and unsaturated polyester composed of
phthalic anhydride, maleic anhydride and propylene glycol (3)
Curing agent (product of Nippon Oils & Fats 0.5 wt % Co., Ltd.,
"Permek N" in commercial designation) having the formula ##STR1##
wherein n is an integer in the range of from 1 to 6 (4) Curing
promoter (product of Japan Chemical 0.5 wt % Industry Co., Ltd.,
"Naphtex Cobalt" (Co 6%) in commercial designation) having the
formula ##STR2## wherein n is an integer of from 1 to 3 Specific
gravity of cured syntactic foam 0.62 g/cc Crushing strength of
cured syntactic foam 1350 kgf/cm.sup.2 (2) (1) Hollow glass
microspheres (specific gravity 35 wt % 0.28) (product of 3M Corp.,
"Glass Bubbles, F29x" in commercial designation) (2) Unsaturated
polyester resin (product of 53 wt % Nippon Shokubai Kagaku Kogyo
Co., Ltd., "Epolac RF1001" in commercial designation) which is a
vinyl ester resin of styrenes and epoxy ester composed of bisphenol
type epoxy resin and methacrylic acid (3) Shrinkproofing agent for
unsaturated 10.0 wt % polyester resin (product of Nippon Shokubai
Kogyo Co., Ltd., "Epolac AT100" in commercial designation)
consisting of styrene monomer solution containing 30% polystyrene
(4) Silane coupling agent (product of Nippon 1.0 wt % Unicar Co.,
Ltd., "Silicone A174" in commercial designation) having the formula
##STR3## (5) Curing agent (product of Nippon Oils & Fats 0.4 wt
% Co., Ltd., "Permek N" in commercial designation) (6) Curing
promoter (product of Japan Chemical 0.6 wt % Industry Co., Ltd.,
"Naphtex Cobalt" (Co 6%) in commercial designation) composed of 55%
methyl ethyl ketone peroxide and 45% dimethyl phthalate Specific
gravity of cured syntactic foam 0.54 g/cc Crushing strength of
cured syntactic foam 1260 kgf/cm.sup.2
______________________________________
The material for the hollow spheres is not limited to ceramics. It
has been confirmed that even when the hollow spheres are made of
glass possessing sufficient resistance to pressure, otherwise
inevitable degradation of strength due to the difference of ratio
of voluminal elasticity between the spheres and the syntactic foam
can be precluded by interposing the empty space along the boundary
of the two components.
Now, the invention will be described more specifically below with
reference to a working example and a comparative experiment.
EXAMPLE
Pressure-resistant hollow spheres having an outside diameter of 96
mm, weight of 171 g, and specific gravity of 0.37 were made of
alumina ceramic having an aluminum content of 84%. (The physical
properties of the alumina ceramic, as determined of test pieces,
were compression strength of 210 kgf/mm.sup.2, bulk modulus of
2.2.times.10.sup.4 kgf/mm, Poisson ratio of 0.19, and true specific
gravity of 3.22). Each of the spheres was produced by forming two
hemispheres by the conventional lathing method, sintering the
formed hemispheres, allowing the sintered hemispheres to cool down,
abrading the edges of the hemispheres, and joining the
hemispheres.
A syntactic foam was obtained by vacuum mixing (1) 32% by weight of
hollow glass microspheres having specific gravity of 0.32 (product
of 3M Corp., "Glass Bubbles, grade D32/4500" in commercial
designation), (2) 67% by weight of unsaturated polyester resin
(product of Nippon Shokubai Kagaku Kogyo Co., Ltd., "Epolac G-82"
in commercial designation), (3) 0.5% by weight of curing agent
(product of Nippon Oils & Fats Co., Ltd., "Permec N" in
commercial designation), and (4) 0.5% by weight of curing promoter
(product of Japan Chemical Industry Co., Ltd., "Naphtex Cobalt" (Co
6%) in commercial designation).
The molding die for the syntactic foam was a block, 110 mm.times.60
mm.times.505 mm in dimension, formed with five regularly spaced 97
mm hemispheres. The aforementioned raw material for syntactic foam
melted by heat was cast in this molding die and then cured.
Consequently, a syntactic foam incorporating semispherical cavities
for admitting hollow spheres was obtained. This syntactic foam was
finished in visible dimensions of 100 mm.times.50 mm.times.500 mm
by cutting the rough edges. Another syntactic foam of entirely the
same shape was produced by repeating the procedure described above.
The two syntactic foam pieces were joined at the portions indicated
by 5 in the drawing, with the aforementioned pressure-resistant
hollow spheres of alumina ceramic placed one each in the spherical
cavities. The spheres were formed by semispheres as illustrated in
FIG. 1. Consequently, an empty space 3 occurred between the
pressure-resistant hollow spheres and the syntactic foam. A
buoyancy material according to this invention was obtained by
forming paths for communication between the empty space and the
outside. The overall specific gravity of this buoyancy material was
0.500 and the apparent gravity including the empty space of this
buoyancy material was 0.493.
This buoyancy material was placed in a high-pressure water tank and
the water pressure applied on the buoyancy material was gradually
increased to test for crushing strength. The syntactic foam in the
material was crushed when the water pressure rose to 1350
kgf/cm.sup.2. Under this pressure, however, the pressure-resistant
hollow spheres of alumina ceramic remained intact. When another
buoyancy material produced by the same procedure was subjected to a
pressure cycle test alternately exposing the material to the
pressure up to 600 kgf/cm.sup.2 and completely relieving the
material of pressure, no abnormal phenomenon developed in the
material until after 2500 cycles.
COMPARATIVE EXPERIMENT
Pressure-resistant hollow spheres of alumina ceramic and a
syntactic foam were produced by faithfully repeating the procedure
of Example. Three buoyancy materials were produced by using the
hollow spheres and the syntactic foam pieces, with adhesive agent
filling the gaps between the pressure-resistant hollow spheres and
syntactic foam as illustrated in FIG. 2.
In the same manner as in Example, the three buoyancy materials were
tested for crushing strength. In all the buoyancy materials, the
hollow spheres of alumina ceramic were crushed under pressure of
200 kgf/cm.sup.2.
All the pressure-resistant hollow spheres of alumina ceramic,
before incorporation in the buoyancy materials, were subjected to a
test of five successive applications of pressure of 800
kgf/cm.sup.2. None of them was crushed. Thus, the difference
between Example and Comparative Experiment was quite distinct.
Since the buoyancy material according to the present invention was
incorporated with paths for enabling the gaps separating the
pressure-resistant hollow spheres of alumina ceramic and the
syntactic foam to communicate with the outside of the material, it
enjoys a notable improvement of crushing strength in spite of a
heavy decline of specific gravity of the syntactic foam to 0.50, a
value even below the lower limit of 0.54 imposed on the
conventional syntactic foam.
Thus, the present invention has realized production of a buoyancy
material having lower specific gravity and higher strength than the
conventional buoyancy material. Thus, it promises to make feasible
the construction of an underwater vehicle for descending to greater
depths.
Although the pressure-resistant hollow spheres used in the working
example and the comparative experiment cited above were made of
alumina ceramic, this invention is applicable to pressure-resistant
hollow spheres made of other material.
* * * * *